Let \(\vec{2i} - \vec{j} - \vec{k}, \vec{5i} + \vec{j} - 2\vec{k}, -13\vec{i} - 11 \vec{j} + 4 \vec{k}\) be the position vectors of three points \(A, B, C\) respectively. If \(\overrightarrow{AB} = \lambda \overrightarrow{BC}\) and \(\overrightarrow{AC} = \mu \overrightarrow{CB}\), then \(\lambda + \mu =\)